Multi-effect desalination apparatus partially dosing acids into some evaporator and desalination method using the same

ABSTRACT

The present disclosure relates to a multi-effect desalination apparatus by partially dosing acids into only evaporators corresponding to a relatively high temperature part, while dosing a polymer-based anti-scalant into all the evaporators, to minimize a risk of a scale and corrosion with maximizing a top brine temperature of desalination facility, and a desalination method using the same.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to Korean Application No. 10-2015-0063983, filed May 7, 2015, the contents of which are incorporated herein in their entirety.

BACKGROUND

The present disclosure relates to a multi-effect desalination apparatus partially dosing acids into some evaporators with high temperature and a desalination method using the same, and more preferably relates to a technique for increasing top brine temperature (TBT) of multi-effect desalination apparatus by additionally dosing acids partially only into the evaporators corresponding to high temperature part (H) to minimize a risk of a scale and corrosion together with an anti-scalant.

Generally, desalination facility is one producing fresh water which can be used as water for living or industrial use from seawater or wastewater, and Multiple Stage Flash (MSF), Multi-effect Distillation (MED), etc. are mostly used, as well as Reverse Osmosis (RO) which uses pressure as a membrane filtration, etc., and Hybrid type, etc. is also used to increase an output of fresh water and effectiveness by mixing two or more of various methods as mentioned above.

Among them, desalination facility by the multi-effect distillation is equipped with evaporator comprised of several effects, and multiple heat exchange tubes wherein steam with high temperature is passed through interior heat exchange space being the interior space of each effect and feed water is sprayed to exterior are equipped.

In addition, each evaporator is constructed so that the steam is fed by connecting to each other by steam feed tube from the first effect, and the produced water generated from each evaporator is connected to a recovery line of fresh water to be discharged by a fresh water pump, a concentrated water with high concentration is discharged to exterior through a discharging.

At first, the steam with the high temperature is fed to the evaporator (100A) of the first effect and feed water is sprayed through the spray nozzle while making the heat exchange on the surface of the heat exchange tube. Therefore, the steam in interior of the heat exchange tube is condensed to make fresh water, simultaneously with generating the steam in the heat exchange space in the interior of the evaporator, and the generated steam acts as a heat source to the evaporator (100B) of the next effect through the steam feed tube and thus the continuous heat exchange can be made to evaporator (100N) of the most downstream.

Various trials have been made to prevent the scale formed by hardness materials included in the feed water in the customary desalination facility such as MED, MSF, and the like. There was a method for inhibiting a formation of scale by treating acid, but since it should accompany an installation of an additional decarbonizing/degassing facility together with the risk problem for corrosion, it was a limited way avoided due to the problem such as the additional electrical power consumption, and thus was disappeared by a development of a polymer-based anti-scalant.

However, the scale risk for evaporator corresponding to ‘high temperature part’ of a number of evaporators, especially the upstream part was not sufficiently resolved only by the newly developed anti-scalant, and thus, since the top brine temperature (TBT) of the desalination facility cannot be set to the constant level or more to drive, there were problems dropping economical efficiency or effectiveness.

Therefore, Laid-open Korean Patent Publication No. 2010-0016519 (‘Desalination apparatus and method’, published on Feb. 12, 2012, etc.) disclose a method for increasing the top brine temperature of the desalination facility by separately installing Nano Filter (NF), RO membrane, etc. on the front of the desalination facility to previously remove the material generating the scale, but, since it needs a large scale of facility for the additional pre-treatment and thus, increases CAPEX and OPEX of all processes, there is a problem that is inefficient.

BRIEF SUMMARY

The present disclosure is provided to solve the above problems, and provides desalination apparatus and method for maximizing the top brine temperature of the desalination facility with minimizing the risk for corrosion and scale by partially dosing acid into only the evaporator relatively corresponding to the high temperature part, while dosing polymer-based anti-scalant into all evaporators.

According to one preferable embodiment of the present disclosure, the present disclosure provides the multi-effect desalination apparatus characterized in equipping with:

multiple effects (100) connected in series which multiple heat exchange tubes are arranged to an interior heat exchange space, the stream with high temperature is passed inside the heat exchange tubes and feed water is fed to the external surface to generate the steam and concentrated water from the feed water through a heat exchange between the steam and feed water; and

a feed water pipe (200) feeding the feed water to each of multiple effects (100) in parallel,

wherein the steam with high temperature is fed to an effect (100A) arranged at the uppermost stream among the multiple effects (100), the steam generated from the feed water through the heat exchange is fed to an adjacent effect (100B) to be made the continuous heat exchange to the effect (100N) arranged at the lowermost stream, and the feed water pipe (200) is equipped with at least one of additive-dosing part (210) for dosing the additive to inhibit the generation of scale in the feed water entering from the exterior, and at least one of pre-heaters (220) for heating the feed water to be entered.

The above additive dosing part (210) can comprise at least one of the first dosing part 1 (211) dosing a polymer-based anti-scalant; and at least one of the second dosing part (212) dosing acid.

It is preferable that the polymer-based anti-scalant is an acrylic polymer comprising ethylenically unsaturated co-monomer as a polymer unit, the acid is selected from an inorganic acid including sulfuric acid, nitric acid or phosphoric acid; organic acid including carboxylic group or suphonic acid group; or the mixtures thereof.

At this time, it is preferable that the first dosing part 1 (211) is equipped to the higher stream than the second dosing part 2 (212) on the feed water pipe (200).

In addition, the anti-scalant dosed from the dosing part 1 (211) is dosed into feed water fed to all multiple evaporators (100), and the acid dosed from the second dosing part 2 (212) is dosed into feed water dosed only into the evaporators (100) corresponding to high temperature part (H), the high temperature part (H) may be some evaporators (100) comprising the evaporator (100A) arranged on the uppermost stream.

At this time, the high temperature part (H) may be at least one of evaporators (100) which the concern of scale formation is risen to the constant level or more to be designated based on a tendency according to the temperature of hardness index representing the concern level of scale or corrosion formation for the feed water calculated by pH value (pH_(s)) when the feed water is saturated by calcium carbonate and pH value (pH_(f)) of the feed water to be measured.

The hardness index may be Ryzar Stability Index (RSI) value calculated by the below mathematic formula 2 or Langelier Saturation Index (LSI) value calculated by the below mathematic formula 3, based on the pH_(s) value and the pH_(f) value calculated by the mathematic formula 1.

pHs=−log(K₂ ^(SW))+log(K_(sp))−log(TA)−log([Ca²⁺])  [mathematic formula 1]

(Wherein, K₂ ^(SW) is the second dissociation constant of carbonic acid, K_(sp) is a solubility product constant of calcite in feed water, [Ca⁺²] is the concentration of calcium ion in feed water, and TA is a total alkalinity.)

RSI=2 pH_(s)−pH_(f)  [mathematic formula 2]

LSI=pH_(f)−pH_(s)  [mathematic formula 3]

In addition, the high temperature part (H) may be the evaporators (100) of some high stream including the uppermost stream evaporator (100A) which the brine temperature is 86 to 110° C., or may be the evaporators (100) of some high stream including the uppermost stream evaporator (100A) which the brine temperature is 65 to 90° C.

Decarbonator (230) and/or deaerator (240) can be equipped on the feed water pipe (200) downstream of the second dosing part (212).

And, the second dosing part (212) can regulate an amount of the acid dosed into the multiple evaporators (100) corresponding to the high temperature part (H) by equipping on the feed water pipe (200) in multiple number.

In addition, the first 1 dosing part (211) and the second dosing part (212) are equipped on the separate feed water pipe (200A, 200B) which are divided separately, and the pre-heater (220) is equipped only on the feed water pipe (200) equipped with the first dosing part (211).

The present disclosure also provides a multi-effect desalination method which comprises:

the first additive-dosing step for dosing a polymer-based anti-scalant into the feed water;

the second additive-dosing step for dosing acid to feed water dosed by the anti-scalant; and

a feed water-feeding step for feeding each of the multiple evaporators (100) in parallel,

in the desalination method using a multi-effect desalination apparatus (Multi-effect Distillator, MED) (A) equipped with the multiple effects (100) connected in series in which multiple heat exchange tubes are arranged to an interior heat exchange space, stream with high temperature is passed inside the heat exchange tubes and the feed water is fed to the external surface to generate the steam and the concentrated water from the feed water through the heat exchange between the steam and feed water, and thus, the steam with high temperature from the exterior is fed to an effect (100A) arranged at the uppermost stream among the multiple effects (100), and the steam generated from the feed water through the heat exchange is fed to an adjacent effect (100B) to be made the continuous heat exchange to the effect (100N) arranged at the lowermost stream.

The anti-scalant dosed in the first additive-dosing step is dosed into the feed water fed into all of the multiple evaporators (100), the acid dosed in the second additive dosing step is dosed only to the feed water feeding into the evaporators (100) corresponding to the high temperature part (H), and the high temperature part (H) may be some evaporators (100) of the upper stream comprising the evaporator (100A) to be arranged in the uppermost stream.

In addition, the high temperature part (H) may be at least one of the evaporators (100) which the concern of scale formation is risen to the constant level or more designated based on a tendency according to the temperature of hardness index representing the concern level of scale or corrosion formation for the feed water calculated by pH value (pH_(s)) when the feed water is saturated by calcium carbonate and pH value (pH_(f)) of the determined feed water.

At this time, it is preferable that the hardness index may be Ryzar Stability Index (RSI) value calculated by the below mathematic formula 2 or Langelier Saturation Index (LSI) value calculated by the below mathematic formula 3 based on the pH_(s) value and the pH_(f) value calculated by the mathematic formula 1.

pHs=−log(K₂ ^(SW))+log(K_(sp))−log(TA)−log([Ca²⁺])  [mathematic formula 1]

(wherein, K₂ ^(SW) is the second dissociation constant of carbonic acid, the K_(sp) is solubility product constant of calcite in the feed water, the [Ca⁺²] is the concentration of calcium ion in the feed water, and the TA is a total alkalinity.)

RSI=2 pH_(s)−pH_(f)  [mathematic formula 2]

LSI=pH_(f)−pH_(s)  [mathematic formula 3]

The high temperature part (H) may be some evaporators (100) of high stream including the uppermost stream evaporator (100A) which the brine temperature is 86 to 110° C., or may be some evaporators (100) of high stream including the uppermost stream evaporator (100A) in which the brine temperature is 65 to 90° C.

The second additive-dosing step may further comprise decarbonating/deaerating step removing carbon dioxide and/or air from the feed water which the anti-scale and acid are dosed.

In addition, the amount of acid dosed into multiple number of evaporators (100) corresponding to the high temperature part (H) may be regulated by dosing acids into the feed water in multiple times, in the second additive-dosing step.

And, a recycling step for recycling all or part of the brine collected from all or some of the multiple evaporators (100) into the feed water and for re-feeding them into the evaporators (100) can be further included.

The condensed water formed by condensing the steam with high temperature fed into the evaporator (100A) arranged on the uppermost stream from exterior through the heat exchange with the feed water can be recovered by dividing independently of the condensed water of other evaporator (100).

The multi-effect desalination apparatus and desalination method using the same of the present invention, as mentioned above, have effects that the risk for scale and corrosion in the desalination apparatus can be minimized by the relatively simple method effectively, the consumed amounts of steam and the material cost of evaporator are saved by raising the TBT and the thermal energy efficiency of the facility can be maximized

BRIEF DESCRIPTION OF THE DRAWINGS

The above and/or other aspects of the disclosure will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:

FIG. 1 is a schematic flow chart of the multi-effect desalination apparatus (A) according to one Example of the present disclosure.

FIG. 2 is a schematic flow chart of the multi-effect desalination apparatus (A) according to other Example of the present disclosure.

FIG. 3 is a schematic flow chart of the multi-effect desalination apparatus (A) according to another Example of the present disclosure.

FIG. 4 is a graph representing RSI value according to the temperature for calculating the brine temperature range of the high temperature part (H) according to Example 1.

FIG. 5 is a graph represent RSI value according to the temperature for calculating the brine temperature range of the high temperature part (H) according to Example 2 of the present disclosure.

FIG. 6 is a flow chart for the multi-effect desalination method according to one Example of the present disclosure.

DETAILED DESCRIPTION

Reference will be now made in detail to embodiments of the present disclosure with reference to the attached drawings. It will be understood that words or terms used in the specification and claims shall not be interpreted as the meaning defined in commonly used dictionaries. It will be further understood that the words or terms should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and the technical idea of the disclosure.

Through the present specification, when any member is posited “on” other members, it also comprises the case that any member is faced on other members as well as the case that another member is present between two members.

Through the present specification, when any part “includes” any constitutive element, it doesn't mean excluding other constitutive elements but it means additionally including other constitutive elements, unless there is any description to the contrary.

The terms “the first”, “the second” and the like are to distinguish one constitutive element from other constitutive element, and are not construed to limit the scope of the present invention. For example, the first constitutive element can be called as the second constitutive element, and similarly the second constitutive element can be called as the first constitutive element.

The terms “maximize,” “minimize” and the like are to be understood as improving, reduce, and so forth and do not require an extreme optimum unless otherwise noted.

Identification code in each of steps is used for convenience of explanation and does not explain the order of each of steps, and each of steps can be practiced differently from the specified order unless the specific order is described in the context. That is, each of steps can be practiced in the order equivalent to the specified order and can be substantially practiced simultaneously with the order and can be practiced on the contrary order.

DESCRIPTION OF REFERENCE NUMERALS USED IN THE DRAWINGS

-   -   A: multi-effect desalination apparatus     -   H: high temperature part     -   100 (100A, 100B, 100C, . . . , 100N): effect     -   200 (200A, 200B): feed water pipe     -   210: additive-dosing part     -   211: dosing part 1     -   212: dosing part 1     -   220: pre-heater     -   230: decarbonator     -   240: deaerator

The present disclosure firstly provides a multi-effect desalination apparatus comprising multiple evaporators (effects) connected in series and, feed water pipes feeding the feed water in parallel. The schematic flow chart of multi-effect desalination apparatus (A) according to one preferable example of the present disclosure is shown in FIG. 1.

In multiple evaporators (100), multiple heat exchange tubes are arranged in the interior heat exchange space, the steam with high temperature is passed through from exterior (steam source) to interior and the feed water is fed to the external surface to generate the steam and the concentrate water (brine) from the feeding water through the heat exchange between steam and feeding water.

The multi-effect desalination apparatus comprising such multiple evaporators (100) can comprise Multiple Stage Flash (MSF) or Multi-Effect Distillation (MED), and in the case of multiple evaporator, it is preferable that it further comprises deaerator.

Specifically, the feed water is fed into the evaporator (100A) arranged at the uppermost stream among multiple evaporators (100) to be directly fed by the exterior steam, the steam generated from it is fed into the interior heat exchange tube of the adjacent next evaporator (100B) to be made the heat exchange again, and finally the continuous heat exchange is made to the evaporator (100N) arranged at the lowermost stream.

At this time, in the feed water pipe (200), at least one of additive-dosing part (210) for dosing the additives (chemical) inhibiting the scale generation into the feed water entering from the exterior is equipped, and at least one of pre-heaters (220) for heating the entered feed water.

Additive dosing part (210) can be constructed with at least one of the first dosing parts (211) dosing a polymer-based anti-scalant and at least one of the second dosing parts (212) dosing acid.

The above polymer-based anti-scalant can use the known high molecular polymer, and can more preferably use acrylic polymer. The used acrylic polymer used at this time can comprise 30 wt % or less, preferably 20 wt % or less, more preferably 10 wt % or less of ethylenically unsaturated co-monomer, based on all ethylenically unsaturated monomer, and the preferable example of the ethylenically unsaturated co-monomer can be methacrylic acid, maleic acid, maleic anhydride, vinylsulphonic acid, allylsulphonic acid and 2-acrylamido-2-methylpropane sulphonic acid and also salts thereof, and the mixtures of such co-monomers can also be comprised (for reference, Laid-open Patent No. KR2014-0003525A of BASP. Co. is added as an example of the polymer-based anti-scalant).

At this time, acid can be partially dosed together with the anti-scalant into the evaporators (100) corresponding to some high temperature parts (H) including the uppermost stream evaporator (100A), while the dosing part 1 (211) is arranged in the upper stream on the feed water pipe (220) than the second dosing part (212) to dose the anti-scalant into the feed water feeding into all evaporators (100A to 100N) through the first dosing part (211).

By limitedly dosing acid into only the high temperature part (H), since the risk of scale can be minimized even for the evaporators (100) effectively set on the high temperature without risk for corrosion, the driving is possible by increasing TBT of all facilities to save the consumed amount of steam and material cost of the evaporator, and since it is more economical due to that the high grade quality of materials for the evaporator and tube can be limitedly used only the high temperature part (H), the heat efficiency can be maximized without any separate additional facility.

The acid used at this time can be selected from various inorganic or organic acids and is not specifically limited. Sulfuric acid, nitric acid, phosphoric acid, etc. can be properly used as the inorganic acid, and organic acid comprising carboxyl group such as acetic acid, oxalic acid, tartaric acid, benzoic acid, etc. or organic acid comprising sulphonic acid group can be properly selected and used as the organic acid, and the mixture thereof can be also used.

In order to increase the top brine temperature by effectively dosing acid to minimize the risk for scale and corrosion of all facilities, it is the main problem how evaporator (100) having the high temperature part (H) is set by dividing the temperature interval.

The high temperature part (H) can be set by using hardness index representing ‘the concern level of scale for feed water or corrosion formation’ calculated by ‘pHs’ value, the pH value when the feed water is saturated by calcium carbonate, ‘pHf’ (f is an abbreviation of the feed water), the pH value of feed water determined in real time.

Specifically, the hardness index has the tendency that the concern level of corrosion is lowered as the temperature is increased, but the concern level for scale formation is increased, and thus, it is preferable to designate the high temperature part (H) to include the high stream evaporators (100), based on the evaporators (100) that the concern of scale formation is increased over a certain level by increasing the temperature of brine from the lowermost evaporator (100N) to the upper stream.

Therefore, since the scale formation risk can be further minimized by additionally dosing acid to the feed water feeding to the evaporators (100) corresponding to the high temperature part, while reducing the risk for scale formation to a certain level together with the risk for corrosion by dosing anti-scalant for the evaporators (100) corresponding to the relatively lower temperature part of downstream, the uppermost stream evaporator (100A) can be driven with more high brine temperature.

Hardness index can be chosen as various forms of index calculated based on pH values and pH_(f) values, and preferably Ryzar Stability Index (RSI) value calculated by the below mathematical formula 2 based on pHs values calculated by the below pHs values or Langelier Saturation Index (LSI) value calculated by the below mathematic formula 3. Besides that, other Carbonate Saturation Indices such as Puckorius Scaling Index (PSI) can be used.

pHs=−log(K₂ ^(SW))+log(K_(sp))−log(TA)−log([Ca²⁺])  [mathematic formula 1]

(wherein, K₂ ^(SW) is the second dissociation constant of carbonic acid, K_(sp) is the solubility product constant of calcite in the feed water, [Ca²⁺] is the concentration of calcium ion in feed water, and TA is a total alkalinity.)

RSI=2 pH_(s)−pH_(f)  [mathematic formula 2]

LSI=pH_(f)−pH_(s)  [mathematic formula 3]

Representatively, in explaining about RSI value, when the calculated RSI value becomes 6 to 7, it can be the feed water of the relatively stable form, when RSI value is increased, the corrosion risk level is gradually increased and when RSI value is lowered, the risk level for scale formation is gradually increased.

Such RSI value is linearly reduced when the temperature is increased by pHs value dependent on the temperature, and when pH value (pHf) of the current feed water is increased, a graph of RSI value according to the temperature is parallelly displaced to (−) direction of y axis (RSI value), and when it is lowered, the graph is parallelly displaced to (+) direction of y axis.

Accordingly, based on the seawater with the inside and outside pH 8 customarily, the concern level for the scale formation can be offset by only the anti-scalant dosed for the down stream evaporators (100) corresponding to the low temperature part, the scale risk of the high temperature part (H) evaporators (100) can be minimized by additionally dosing acid for the evaporators (100) corresponding to the high temperature part with the constant temperature more to parallelly displace the graph for RSI value according to the temperature to (+) direction of y axis to control the RSI value to correspond to the stable region being 6 to 7, and thus, since the high temperature part (H) can be set to the high temperature, the driving to the increased top brine temperature is possible.

-   -   Meanwhile, the decarbonator (230) and deaerator (240) for         removing carbon dioxide and air generated due to dosing of acid         can be equipped on the feed water pipe (200) of the downstream         of the second dosing part (212). Such decarbonator (230) and         deaerator (240) can be constructed with the separate divided         unit, and can be constructed with the unit integrated to perform         both roles in one unit. Since it is sufficient to dose acid only         for a flow rate fed to the high temperature part (H) in relative         to the customary facility which has to control the scale only by         dosing acid, it is economical due to that the size of facility         such as a booster pump including decarbonator (230) or deaerator         (240) is reduced.     -   Thus, carbon dioxide (CO2), etc. additionally generated by         increasing of TBT and dosing of acid can be used in         post-processing facility such as Remineralization plant, and the         like.     -   The risk for scale and corrosion can be in real time in coping         with the situations varying according to the conditions of the         original water by controlling the amount of anti-scalant or acid         to be dosed to the feed water so that the first dosing part         (211) or the second dosing part (212) is plurally equipped on         the feed water pipe (200) or is constructed to be installed with         pipes which can be dosed on many parts, when it is singularly         composed, wherein the position monitoring the condition of the         original water can properly selected in front of and/or behind         pre-heater (220) in feed water pipe (200).     -   In addition, it can be controlled for anti-scalant to be dosed         once again to the evaporator (100) corresponding to middle         temperature part by additionally sorting the classification of         evaporators (100) according to the manner of temperature         intervals as the high temperature part (H) as well as middle         temperature part, lower temperature part, etc., as well as, as         shown in FIG. 2. The facility can be effectively operated by         sorting the evaporators (100) into plural groups to properly         control the dosing amount of anti-scalant and acid to the scale         risk according to the temperature, salinity, etc.     -   In addition, the flow rate, or temperature, etc. of the feed         water to be dosed into the temperature part (H) and feed water         to be dosed into the evaporators (100) not the high temperature         part (H) can be effectively controlled by gradually equipping         the first dosing part (211) and the second dosing part (212) on         the single feed water pipe (200), as well as by sequentially         equipping the first dosing part (211) and the second dosing part         (212) on the feed water pipe (200A, 200B) which are separately         divided. In this case, the thermal efficiency can be optimized         by equipping the pre-heater (220) only on the feed water pipe         (200A) to be dosed into the evaporators (100) not the high         temperature part (H).     -   Meanwhile, when the risk for scale formation is somewhat less         according to the situation of feed water or the operation         condition, the amount of the used anti-scalant and acid can be         reduced in the first dosing part (211) and the second dosing         part (212) by recycling all or some of concentrated water         comprising anti-scalant or acid, as discharged from the         evaporator (100) and re-utilizing the anti-scalant and acid         component comprised therein. Specifically, the concentrated         water in the evaporator (100) of the high temperature part (H)         treated with acid is re-utilized by recycling into the feed         water pipe (200) to be dosed into the high temperature part (H),         and it can be re-dosed from the feed water pipe (200) by         partially recycling the concentrated water of the evaporator         (100) corresponding to the low temperature part.     -   Also, when the high temperature steam is fed from the exterior         steam source generally made from Power plant, etc., since the         final treated water can be contaminated by various harmful         materials, additives, etc., comprised in the steam, a steam         transformer is to be equipped in order to primarily secure the         making of the drinking water in hybrid facility fused with Power         plant and multi-effect desalination facility. But, since the         present invention can exclude TVC or steam transformer by         separately isolating and recovering the condensed water to be         formed in the uppermost stream evaporator (100A) fed with the         vapor directly from exterior, from other evaporators (100), to         conduct the role of the steam transformer, the change of load         can be easy and the loss of temperature can be minimized     -   Hereinafter, examples for the multi-effect desalination         apparatus partially dosing acids into some evaporators with high         temperature of the present invention and the desalination method         using the same will be explained. However, since it is merely         the most preferable example of the present invention and does         not represent all of the technical ideas, it is to be understood         that various equivalents and modification examples which are         able to replace them can be present.

Example 1 Setting 86˜110° C. as the Brine Temperature of the High Temperature Part (H)

-   -   Generally, the top brine temperature has been limited to less         than about 70° C. in MED facility due to the concern of scale         formation, but the top brine temperature of MED facility can be         greatly raised at least 5° C. or more by partially dosing acid         in the present disclosure, and the top brine temperature can be         about 75˜130° C. according to the saline condition, the dosing         amount of acid, the system planning, etc.     -   Specifically, the multi-effect desalination apparatus (A) can be         operated by setting the evaporators (100) of the upper stream         with the brine temperature of 86˜110° C. according to the         Example 1 of the present disclosure.     -   Referring to FIG. 4, the ordinary seawater without dosing acid         exhibits pH value of about 8.2, but since RSI value is lower         when it reaches the level of about 86° C., the risk of the scale         formation cannot be offset only by dosing the anti-scalant. When         the pH value of the seawater is lowered to about pH 5.6 with         dosing the proper amount of acid to the extent that the risk of         corrosion is not present by setting the high temperature         part (H) from the evaporators (100) corresponding to such zone,         since the stable operation is possible by minimizing the scale         risk, the top brine temperature can be increased to about 110°         C.

Example 2 Setting 65˜90° C. as the Brine Temperature as the High Temperature Part (H)

-   -   Meanwhile, although the present disclosure greatly lowers the         brine temperature of the high temperature part (H) according to         example 2, its proper input amount of acid and the point to be         dosed, etc. can be effectively calculated.

Specifically, the multi-effect desalination apparatus (A) can be operated by setting the evaporators (100) of the upper stream which the saline temperature is about 65˜90° C. as the high temperature part (H), and the operation of the facility can be effectively made without any risk of scale and corrosion by controlling the scale risk raised around the saline temperature of about 65° C. to the stable interval.

Further, the embodiments discussed have been presented by way of example only and not limitation. Thus, the breadth and scope of the invention(s) should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents. Moreover, the above advantages and features are provided in described embodiments, but shall not limit the application of the claims to processes and structures accomplishing any or all of the above advantages.

Additionally, the section headings herein are provided for consistency with the suggestions under 37 CFR 1.77 or otherwise to provide organizational cues. These headings shall not limit or characterize the invention(s) set out in any claims that may issue from this disclosure. Specifically and by way of example, although the headings refer to a “Technical Field,” the claims should not be limited by the language chosen under this heading to describe the so-called technical field. Further, a description of a technology in the “Background” is not to be construed as an admission that technology is prior art to any invention(s) in this disclosure. Neither is the “Brief Summary” to be considered as a characterization of the invention(s) set forth in the claims found herein. Furthermore, any reference in this disclosure to “invention” in the singular should not be used to argue that there is only a single point of novelty claimed in this disclosure. Multiple inventions may be set forth according to the limitations of the multiple claims associated with this disclosure, and the claims accordingly define the invention(s), and their equivalents, that are protected thereby. In all instances, the scope of the claims shall be considered on their own merits in light of the specification, but should not be constrained by the headings set forth herein. 

What is claimed is:
 1. A multi-stage desalination apparatus, comprising: a plurality of evaporator stages arranged in series, the evaporator stages respectively including heat exchange tubes disposed in interior heat exchange spaces, the plurality of evaporator stages being operable to pass steam with a high temperature inside the heat exchange tubes and feed feed water to an external surface of the heat exchange tubes to generate the steam and concentrate water from the feed water through a heat exchange between the steam and feed water; and a feed water pipe operable to feed the feed water to each of multiple evaporator stages in parallel, wherein the steam with high temperature is fed to an evaporator stage arranged at an uppermost in a stream among the multiple evaporator stages, the steam generated from the feed water through the heat exchange is fed to an adjacent evaporator stage to provide a continuous heat exchange an evaporator stage arranged at the lowermost stream, the feed water pipe includes at least one additive-dosing part operable to dose an additive to inhibit the generation of scale in the feed water, and the feed water pipe includes at least one pre-heaters operable to heat the feed water to be entered.
 2. The multi-stage desalination apparatus according to claim 1, wherein the additive-dosing part includes at least one first dosing part operable to dosing a polymer-based anti-scalant and at least one second dosing part operable to dose acid.
 3. The multi-stage desalination apparatus according to claim 2, wherein the first dosing part is arranged upstream of the second dosing part on the feed water pipe (200).
 4. The multi-stage desalination apparatus according to claim 2, wherein the first dosing part is arranged to dose the anti-scalant into the feed water of all of the evaporator stages, and the second dosing part is arranged to dose the acid only into the feed water of evaporator stages associated with a higher temperature part.
 5. The multi-stage desalination apparatus according to claim 4, wherein the high temperature part includes at least one of the evaporator stages designated based on a tendency to scale formation according to the temperature of hardness index for the feed water calculated by pH value (pH_(s)) when the feed water is saturated by calcium carbonate and pH value (pH_(f)) of the determined feed water, the hardness index is a Ryzar Stability Index (RSI) value calculated by a second formula or a Langelier Saturation Index (LSI) value calculated by a third formula based on the pH_(s) value and the pH_(f) value calculated by a first formula, the first formula is pHs=−log(K₂ ^(SW))+log(K_(sp))−log(TA)−log([Ca²⁺]), wherein, K₂ ^(SW) is the second dissociation constant of carbonic acid, K_(sp) is solubility product constant of calcite in feed water, [Ca⁺²] is the concentration of calcium ion in feed water, and TA is a total alkalinity, the second formula is RSI=2 pH_(s)−pH_(f), and the third formula is LSI=pH_(f)−pH_(s).
 6. The multi-stage desalination apparatus according to claim 4, wherein the high temperature part includes upper stream evaporators stages including an uppermost stream evaporator in which abrine temperature is in the range of 86 to 110° C.
 7. The multi-stage desalination apparatus according to claim 4, wherein the high temperature part includes upper stream evaporators stages including an uppermost stream evaporator stage in which a brine temperature is in the range of 65 to 90° C.
 8. The multi-stage desalination apparatus according to claim 2, wherein the feed water pipe includes at least one of a decarbonator and a deaerator arranged downstream of the second dosing part.
 9. The multi-stage desalination apparatus according to claim 4, wherein the second dosing part is operable to regulate an amount of the acid dosed into multiple evaporator stages corresponding to the high temperature part (H) by equipping on the feed water pipe (200) in multiple numbers.
 10. The multi-stage desalination apparatus according to claim 2, wherein the first dosing part (211) and the second dosing part (212) are equipped on the separate feed water pipe (200A, 200B) which are divided separately, and the pre-heater (220) is equipped only on the feed water pipe (200) equipped with the first dosing part (211).
 11. A multi-stage desalination method, comprising: a first additive-dosing step of dosing a polymer-based anti-scalant into a feed water; a second additive-dosing step of dosing acid to feed water dosed by the anti-scalant; and a feed water-feeding step of feeding each of the multiple evaporators (100) in parallel, wherein the plurality of evaporator stages are arranged in series, the evaporator stages respectively including heat exchange tubes disposed in interior heat exchange spaces, the plurality of evaporator stages being operable to pass steam with a high temperature inside the heat exchange tubes and feed feed water to an external surface of the heat exchange tubes to generate the steam and concentrate water from the feed water through a heat exchange between the steam and feed water, the steam with high temperature is fed to an evaporator stage arranged at an uppermost in a stream among the multiple evaporator stages, and the steam generated from the feed water through the heat exchange is fed to an adjacent evaporator stage to provide a continuous heat exchange an evaporator stage arranged at the lowermost stream.
 12. The multi-stage desalination method according to claim 11, wherein the polymer-based anti-scalant is an acrylic polymer including ethylenically unsaturated co-monomer as a polymer unit, and the acid is selected from the group consisting of an inorganic acid including sulfuric acid, nitric acid or phosphoric acid, an organic acid including carboxyl group or suphonic acid group, and mixtures thereof.
 13. The multi-stage desalination method according to claim 11, wherein the first additive dosing step includes dosing the anti-scalant into the feed water of all of the evaporator stages, and the second additive dosing step includes dosing the acid only into the feed water feeding into evaporator stages associated with a higher temperature part.
 14. The multi-stage desalination method according to claim 13, further comprising designating at least one of the stages to be in the high temperature part based on a tendency to scale formation according to the temperature of hardness index for the feed water calculated by pH value (pH_(s)) when the feed water is saturated by calcium carbonate and pH value (pH_(f)) of the determined feed water, wherein the hardness index is a Ryzar Stability Index (RSI) value calculated by a second formula or a Langelier Saturation Index (LSI) value calculated by a third formula based on the pH_(s) value and the pH_(f) value calculated by a first formula, the first formula is pHs=−log(K₂ ^(SW))+log(K_(sp))−log(TA)−log([Ca²⁺]), wherein, K₂ ^(SW) is the second dissociation constant of carbonic acid, K_(sp) is solubility product constant of calcite in feed water, [Ca⁺²] is the concentration of calcium ion in feed water, and TA is a total alkalinity, the second formula is RSI=2 pH_(s)−pH_(f), and the third formula is LSI=pH_(f)−pH_(s).
 15. The multi-stage desalination method according to claim 13, wherein the high temperature part includes upper stream evaporators stages including an uppermost stream evaporator in which a brine temperature is in the range of 86 to 110° C.
 16. The multi-stage desalination method according to claim 13, wherein the high temperature part includes upper stream evaporators stages including an uppermost stream evaporator in which a brine temperature is in the range of 65 to 90° C.
 17. The multi-stage desalination method according to claim 12, wherein the second additive-dosing step includes a decarbonating or deaerating step removing at least one of carbon dioxide and air from the feed water to which the anti-scalant and acid are dosed.
 18. The multi-stage desalination method according to claim 13, wherein, in the second additive-dosing step, an amount of the acid dosed into multiple evaporators stages corresponding to the high temperature part is regulated by dosing acids into the feed water multiple times.
 19. The multi-stage desalination method according to claim 12, further comprising a recycling step of recycling at least some of brine collected from at least some of the evaporator stages into the feed water for re-feeding to the evaporator stages.
 20. The multi-stage desalination method according to claim 12, further comprising recovering condensed water formed by an uppermost stream evaporator stage by independently dividing the condensate water of other evaporator stages. 